Charred documents are the burnt documents that have turned black and fragile due to the application of excessive heat to the documents. The decipherment and handling of charred documents is one of the complex problems in questioned documents examination.
Deciphering a burnt document has turned to be of great importance as they can reveal a lot of information in the ongoing investigation. This process is also one of the most difficult one due to the sample’s fragile nature. If handling and separation is not done properly, the sample can be of zero value.
Methods to decipher Charred documents
The deciphering methods of Charred documents have been classified into two categories i.e., Photographic and Visual methods.
These methods require pure photographic techniques to reveal the content of the burnt documents. The different photography methods used in deciphering are:
I. Contact Process
Davis of Bureau of Standards conducted various experiments that have revealed that the recently burned documents emit gases which are capable of recording an image in photographic emulsion. Several other experiments also revealed that the ink, pencil, etc. when placed on the paper before burning inhibits the gases to release and so when developed and photographed in a fixed proper photographic manner can reveal an image similar to ordinary photographic negative.
John F. Tyrrell conducted an experiment in which he burned a stack of documents in a container and when deciphered with the use of this method revealed 85% of the contents in the documents.
This method has a disadvantage of being a time-consuming method and can take weeks to decipher the charred documents.
II. Filter Photography
This methods requires the use of a Wratten deep blue filter along with the commercial film. The function of the film is not utterly known, however, it seems to intensify the variations in the actinic power of burnt documents background as compared to the parts of paper on which the ink has been deposited.
This method is somewhat faster than the contact process.
III. Infrared Photography
It is one of the highly preferred methods among the three to decipher the burnt documents. However, it is also not completely dependable as most of the samples fail to yield satisfactory results as opposed to some which provide astonishing results especially when the writing is done with pencil, typewriter, or dense iron-gall ink.
This method utilizes the use of a Wratten F Red filter along with Eastman infrared plates carried out in Eastman DK 50 filter. The Wratten F Red filter was later replaced by 87 infrared filter.
Visual Deciphering Methods
The main purpose of using Visual methods is to decipher large number of documents which would be expensive as well as time-consuming with photographic methods alone. The different Visual Decipherment methods are:-
I. Reflectivity Method
It is one of the most easiest and versatile deciphering technique. In this technique, the documents are examined by a controlled light source in which the examiner looks on the charred document from various different angles.
The success of this technique depends on the density of the writing instrument and the degree of burning. There is no rule to look at the charred document from a particular angle. In some cases, angle-view produces good results while in some cases oblique lightning produces good results.
However, the most effective way is to use the oblique lightning and place the charred document between two clear glasses while carefully pressing the two halves together and bind at the edge with the scotch tape. The protected fragments in this way presents a permanent record as well as flatted in a way that they can be examined more pomptly.
II. Alcohol-Glycerin Immersion method
In this method, the charred documents are immersed in a Glycerin-alcohol-water solution for varying periods of time and the experiments have deciphered 90% of the contents of the documents. The components of this solution include 2 parts of water, 5 parts of alcohol and 3 parts of glycerin.
III. Silver-Nitrate method
This technique was discovered by Cherill of Scotland, who used this technique when all other deciphering methods have failed. In this method, the carbonized paper is placed at the bottom of the photographic processing pan.
A solution of 5% aqueous Silver Nitrate is poured over the fragment and the second glass plate is then placed over top of the fragment. The fragments treated must not be kept in direct contact with the sunlight. Any writing present then will be visible within 2-3 hours as a black image against the grey background.
If the original writing is weak, a weaker solution with longer development is recommended. The developed image can be photographed for future purposes.
IV. Chloral Hydrate Treatment
This method was discovered by H.J. Walls & W.D. Taylor during the World War II. In this method, a 25% Chloral hydrate solution in the alcohol is applied to the charred document using a camel hair brush or the sample is immersed in the chloral hydrate solution.
The sample is then placed on a heat resistant plate in an oven heated at 60 degree celsius. When the solution is dried, the same process is applied to the sample several times. During the last time,the chloral hydrate solution is mixed with 10% glycerin and the same process is carried out.
This gradual process creates a clarifying action on the burnt figures or letters. Many inks have responded well to this treatment except washable analine inks.
V. Pottasium-Ferrocyanide Treatment
Most of the inks used nowadays have Iron embedded in them and a chemical reaction with Iron causes a color reaction. Therefore, residues of iron in the ink can be used to react positively to the charred document.
The chemical Pottasium Ferrocyanide when combined with 2% of Hydrochloric acid produces a bright blue colored writing if the ink is iron base. However, an alternate approach has been found to be more succesful.
Apply a soaked blotting paper in Pottasium Ferrocyanide solution against the back of the charred document and then place a white sheet of paper at the face of the charred document in close contact. If the ink is of Iron base, a Prussian blue color appears on the white sheet in a reversed outline of the writing.
VI. Fluorescence in UV Light
This method was discovered by Julius Grant of Great Britain. He discovered that when the charred document is saturated with a solution of Pale mineral oil and Petroleum spirit, a fluorescent differentiation between writing and paper can be created when viewed under filtered UV light.